The present invention relates to communication apparatus and, more particularly, to a half-duplex digitally-controlled telephone communication apparatus.
There are many telephone communication systems in which it is desired for one subscriber to communicate with another subscriber using sampled voice data which is processed in real time in a digital format and transmitted over telephone lines via modem equipment and re-processed at the receiving end for use by the other subscriber. In half-duplex systems of this type it is a requirement that the modulated data originating at one subscriber location not be present on a telephone line simultaneously with modulated data originating at the other subscriber location so as to prevent the data on the line from being undesirably combined. In this latter situation, combined modulated data received by a demodulator would lead to an error rate higher than normally expected in a well-designed communication system and, when processed by a speech synthesizer, could result in a distorted version of the desired output, thereby rendering the communication channel deficient or impossible to use for speech communication. Consequently, in this type of system it is desirable that one speaker maintain control of the line for so long as he is speaking and relinquish the line to the other speaker only upon termination of his speech. It is further desirable and important that no part of the speech of either speaker be lost to the other, for example, due to delays in the system in detecting the onset of speech data, or that the line be undesirably switched from one speaker to the other during normal pauses as occur during normal conversation.
The present invention is directed to communication apparatus which satisfies the abovementioned requirements or criteria.